1. Technical Field
The present invention relates to a projection zoom lens system having a five-group configuration in which three groups are movable for zooming and mounted in a projection type display apparatus and to the projection type display apparatus having the projection zoom lens system. In particular, the invention also relates to a projection zoom lens system and a projection type display apparatus configured so that rays containing image information, which are generated from a light valve such as a transmissive or reflective liquid crystal display device or a DMD (Digital Micromirror Device) display device, are projected and magnified on a screen.
2. Related Art
In recent projectors, a projector having a configuration in which three light valves corresponding to illuminating rays of RGB three primary colors are employed is used. The rays modulated by the respective light valves are synthesized by a prism or the like. And an image is displayed on a screen through a projection lens.
Recently, a decrease in size and an increase in accuracy rapidly progress in the light valve mentioned above. Besides, with an increase in spread of PCs, the demands of performing presentation using such a projector increase. Hence, needs for a more high-performance and more small-sized lightweight projector arise. Accordingly, it is necessary for the projections lenses to satisfy the needs.
However, in a projector that synthesizes and projects the rays modulated from the three light valves by using a color synthesizing optical system, a projection lens system is in need of a long back focal length for disposing a prism and the like which synthesize colors. Furthermore, in a color synthesizing optical system, spectrum characteristic thereof is changed depending on an incident angle of incident rays. Thus, the projection lens system is required to have telecentricity, which is a property of a telecentric system in which an entrance pupil is sufficiently far away in view from reduction side. Further, there are required lens speed and aberration correction appropriate to resolution of an image pickup device, and in the case of front projection type, there are also required a zoom function and a wide angle of view in terms of installation. In addition, according to a decrease in size of the light valve, an increase in demand for mobile applications, and reduction in price of the apparatus, similarly to the other members, the projection lens system also has been strongly required to be reduced in size and weight.
As projection lenses satisfying the requirements mentioned above, there have been known projection lens systems configured such that five groups of negative-positive-positive-positive-positive or negative-positive-positive-negative-positive are arranged in order from the magnification side. In the lens system, during zooming, the first lens group and the fifth lens group remain stationary while the second lens group, the third lens group, and the fourth lens group are movable in an optical axis direction. Such projection lens systems are disclosed in Patent Documents 1 (JP-B-3954736) and 2 (JP-A-2006-162734 corresponding to US 2006/139766 A).
However, the projection lens systems disclosed in Patent Documents 1 and 2 are not enough to satisfy the recent strong requirement for projection lens systems in view of balance of various aberrations.
Meanwhile, if the possibility of optical design is expanded, for example, by increasing the number of lenses or lens groups movable for zooming, it is possible to improve lens performance. However, when lens performance is improved depending on such an increase in the number of components, increases in size and cost is directly caused, and a thickness of glass material increases in the whole lens system, thereby causing deterioration in spectral transmittance. The deterioration in spectral transmittance is remarkable in a short wavelength range, and becomes a disadvantageous factor particularly in a projector incapable of controlling directly an image which is projected after passing through a projection lens.
Furthermore, to use aspheric surface is a means for correcting aberrations. By replacing a plurality of spherical lenses by one aspheric lens, it is possible to downsize an optical system while maintaining performance thereof.
Meanwhile, an aspheric lens is required to have high precision in component and assembly, and thus if many aspheric lenses are used, problems arise in that difficulty in manufacture increases, and small lot production causes disadvantage in cost.
Accordingly, in an actual lens design, it is necessary to develop a lens configuration capable of obtaining high optical performance required for projection lenses while satisfying various requirements such as a decrease in size, reduction in cost, and mass productivity.
The present invention has been made in consideration of the above-mentioned situation, and its object is to provide a projection lens system capable of obtaining high optical performance while satisfying requirements such as a decrease in size, reduction in cost, and mass productivity required for recent projections lenses, and to provide a projection type display apparatus using the projection lens system.